David stoddart



DAVID s'roDDART, or sAN rRANcrsco, cALIroRNr `VALVE-enna ron STEAM-Encinas."

specification lof Letters Patent No. 26,301, datedirovemtef2951859.

To @ZZ whom it may concern: y, y

Be it known that I, DAVID SToDDAR'r, of the city andcounty `of San Francisco and State of California, have invented a .new

and Improved Adjustable Gut- Oif for `Steamllngines; and I do hereby declare that the `following' is a full and exactdescription of the same, reference` being had to the accompanying drawings and tothe letters of reference marked thereon.` y

The purpose of my invention is thel usual oflice of a steam-engine cut-off, to fopen the steam valve at the commencement of a stroke, and afterward close it again at some required period of "the stroke, and thus permit the steam to work eXpansively. y

The accompanying drawings illustrate the invention asV applied in `the. manner I believe to be the best.

Figure 1, shows its attachment to the puppet valves of a Mississippi steamboat engine.

A and B are two cams `of a well known shape, commonly called my full stroke cams. B has only one-half as much throw as A.

C and D are the cam yokes.

E is a rocking bar, which is so connected to the yokes that it may vibrate as they move, and transmit its motion to the valverock-shaft through the cam rod F. E is connected to D at the center, to C at `one extremity, and to F at the other extremity.

The cam A is fixed permanently to the shaft, and its office is `to open the valve. The cam B is free to be turned around on the shaft, and fastened by the bolt Gr to the other cam at any required position; its

oflice is to close the valve, and the period of closing or cutting oft is governed by its position on the shaft. In the drawing it is set to cut-0E about half stroke.

The o eration of the contrivance is thus, the sha tturns as the arrow shows, and A moves its yoke and opens one of the valves, and then following after it B moves its yoke `and shuts the valve, then both yokes continue stationary until A reaches the opposite side of its yoke and moves it in the other direction to open the` other valve, which in like manner is closed by B, and a period of rest for the yokes again occurs, until the engine Areaches its original position, having performed one revolution. This alternation of motion and rest will be clearly apprehended on discussing the construction of the full stroke cam, see Fig. 2, required, to draw a full stroke cam that throw. Draw the lnf fquallt `the give diameter f of the yoke, fin making a c equal to thelgiven ,throw bisea t a at rfid adatta a ma; radii to describe the `cilifves.woifffth From the samefcenter rldescribeftwo circ with the radii Z @,rZ Z9,ass`1`nnetliefpoin` in the larger circle as a center` andwith will always fill the yoke. ySuppose to `1re volve `as the arrow shows#I So long Casa point of `the curve betweenojand Z @110,11

from the center-J1", nomotion; tlieulyoke take place untilgthe pointfZ reaclies until the point Z reaches 7a', and commences ythe throw in the opposite direction.

Refer again to Fig. 1. It is necessary my inventionthat the "yokelofvthecamyB :1 should be at rest at theyinstant` whenthe cam A commences to open` the valve, so as to maintain the same lead in all cases; there-I fore B should neverbe ahead lofA, so as Q to begin its closingqaction, before `A` has f begun toopen the `valveynorfshould it befgo. will be completed beforeA begins to open f" VVhenwthe lines WZ i111` both cams coincide `the steamvalve will not open at all, and when o" m in `B coincide 15505 stroke, `and again the cut-off will @take place according'` to `any relative position. of`

the cams between these limits;` Withlthe y. full-stroke cam, the smallerthe throw in "l proportion to the diameter, the smaller willglm.)l be the angle Z r m, and the quicker will beg so far behind A, but thatts clit-oif action the opposite valve.

with r n in A, the enginewill-work fullwill ll al given and fa"givenf` ein i he ich: m as the center describen;ol.` The sh ded port-ion `(Z m n o) is ltliexrequired;fcamfwh' h the action of the cam. I `,employthisprinf` 1 ciple to obtain the quickest possible closing` be adjustable and the "closing cam, `preserviio ing the connections to thefrocking bar as l 1m j;

they are.

The effect would be to open `thef valve quicker than the., first arrangement CTI which is not required, and also to close it slower which is a disadvantage. B having the smaller throw should always be the cutoli" cam. Again, A and B might be made with an equal throw and the rocking bar be connected to the yokes at its extremities and to the cam rod at its center. In this case the opening and closing motions would be alike, and both slower than the opening motion of the rst arrangement, because the cams would require to have twice the throw of the pin in the rock-shaft-arm whereas in Y' the first arrangement the throw of A is only one-half the throw of the said pin. The arrangement in Fig. l is then the best because, while it opens the valve quickly, it closes it with greater rapidity than either of the other modes. It is not necessary that B should have just one-half the throw of A, it might have somewhat more or less, and its yoke be connected to the rocking bar above or below the center, in proportion' to the throw. Proper mechanism could be employed, whereby the cam B could be adjusted while the engine is in motion.

Figs. 3, 4, 5 and 6 represent different positions of a slide valve wherein the exhaust port remains open after the cut-off has taken place, 4 and 5 are the positions of extreme throw, and 3 and 6 the cut-o' positions. This motion for such a valve is not new and it only remains for me to show how to obtain such a motion from my device. |The motion of an assumed point in the valve may be represented in direction and extent by the arrows in Fig. 7. The long black arrow shows the opening throw and the short red arrow the return or cut-off throw for one steam port, and the long red and short black arrows show like motions for the other steam port; the distance between the two dotted lines is the distance between the cut-olf positions which we will call p, and let g be equal to the length ofone of the long arrows. I recommend the same arrangement as in Fig. l, with this difference that the cam B should have a less throw than one half that of A, to obtain the proper cut-off positions. Construct the cam A with its throw equal to g and then the throw B will be equal to g/Q-p/Q.

Claim. f

I do not claim the usek of two cams to work the steam valve, but I claim the use of the fixed cam A, in combination with the adjustable cam B, and the rocking bar E, which is connected to the cam rod, and also connected to and operated by the cam yokes substantially in the manner described.

DAVID sT'oDDART.

Witnesses: Y

ELIZA J. S'roDDART, ROBERT STODDART. 

